1. Field of the Invention
The present invention relates to vacuum molding a vehicle tire. In particular, the present invention relates to venting to atmosphere a recess in a tire mold for forming a marking on the tire, such as a raised white letter or a white sidewall.
2. Description of the Prior Art
Vacuum molding systems for a vehicle tire are known. One such vacuum molding system is disclosed in U.S. Pat. No. 4,597,929. The vacuum molding system disclosed U.S. Pat. No. 4,597,929 includes a mold having a surface defining a cavity for receiving and shaping an uncured tire. An inflatable bladder presses the uncured tire against the surface defining the cavity. As the uncured tire is being pressed against the surface defining the cavity, a vacuum source is actuated. The vacuum source removes air from between the external surface of the tire and the surface defining the cavity. The tire is then cured by heat and pressure.
There are often relatively deep blind pockets or recesses extending from the cavity. The deep recesses are for forming some marking on the side of the tire, such as a raised white letter or a white sidewall. If air is not sufficiently evacuated from each recess, a blemish in the marking may result. The blemish occurs when the uncured tire is pressed against the surface defining the cavity and seals off the recess from the vacuum source. When the recess is sealed off, evacuation of air from the recess is blocked. The air in the recess prevents a portion of the marking from completely filling the recess and engaging all of the surfaces defining the recess. Thus, proper curing of that portion of the marking may be prevented which can result in a buildup of deposits in a portion of the recess.
One resolution to the problem of a sealed recess is to fluidly connect the recess with the vacuum source through a passage. A vent plug is inserted in the passage adjacent the recess to limit the flow of rubber into the passage. The vent plug often becomes clogged with cured rubber and must be removed from the passage to provide effective venting of the recess. However, the vent plug is often difficult to access and removal is a cumbersome and labor intensive operation.
Another resolution to the problem of a sealed recess is to vent the recess to the exterior of the mold and to atmosphere through a passage. However, if the flow of air from atmosphere through the passage is not restricted during the evacuation cycle, before the recess is sealed off by the uncured tire, too much air can enter the cavity. This burdens the vacuum source and reduces the effectiveness of the vacuum molding system. One way to minimize the flow of air into the cavity is to insert a vent plug in the passage. However, the problems associated with clogging and accessibility of the vent plug occurs, as described above. Furthermore, the opening in known vent plugs are relatively large and do not sufficiently limit air flow into the cavity. For example, U.S. Pat. No. 4,436,497 discloses a vent plug having an opening with a diameter of approximately 0.024 inch. Other vent plugs are known which have an opening with a diameter of approximately 0.015 inch. This size opening yields an area for air to flow through of approximately 0.00018 square inch.
U.S. Pat. No. 4,021,168 discloses a restrictor located in a passage which communicates the sidewall area of the tire mold with the exterior of the mold. The restrictor extends substantially the entire length of the passage. The restrictor must be removed from the mold in a direction toward the cavity and not toward the exterior of the mold. The head of the restrictor forms a recess in the exterior of the tire which may be visually objectionable.